How to replace / swap frames in Blender VSE?
I did this only a day ago.  I'd changed the path where the videos were stored, and the strip after that went blank.  I pressed "N" from the VSE window, went to the right where the strip's properties showed up and clicked on the source folder, browsed for the new path, and bingo, that video came back with fading settings, keyframes etc, intact!

Hope this is all you need to do.  Just re-browse to the desired video.  If they all have the same number of frames you might get away with this.

An alternative might be to produce just the best quality video and convert/copy that to lower settings for preview etc.